In modern motor vehicles, particularly passenger motor vehicles, automated couplings are used increasingly.
By using such clutches not only in connection with automated gearshift transmissions but also with manually operated gearshift transmissions, one has the advantage of improved driving comfort, as shown by experience, particularly in connection with automated gearshift transmissions; a further advantage is that one drives more frequently in gears with long transmission ratios, thus reducing fuel consumption and environmental pollution. FIG. 1 shows the design of a vehicle drive train with a common automated clutch.
Engine 10 is connected via the clutch 12 with manual shift transmission 14 that in the depicted example is connected via cardan shaft 16 with differential unit 18 again connected via cardan shaft 20 with rear wheels 22.
It is obvious that the drive train could be used for a vehicle with front drive or all-wheel drive.
Clutch 12 is actuated by an actuating device and/or actuator 24. Manual-shift transmission 14 involves, for instance, an automated manual-shift transmission that is actuated by actuating device 26. Selection unit 28 is provided for operating the transmission with which different driving programs or gears can be selected. Accelerator pedal 30 connected directly or via control unit 32, or via a control device with power adjustment element 34 of engine 10 is used to control the load of engine 10. Control unit 32 is connected to sensors such as sensor 36 for acquiring the rotation speed of a flywheel of engine 10 or an input shaft of clutch 12, sensor 38 for acquiring the rotation speed of a clutch disc—not depicted—which is connected non-rotatably with an output shaft of the clutch or an input shaft of transmission 14, rotation speed sensors 40 for acquiring the wheel rotation speeds as well as other sensors, for instance a coolant temperature sensor, a sensor for acquiring the position of power adjustment element 34, a sensor for acquiring the position of the clutch etc. The programs with which actuating device 26, the actuator 24, and actuator for power adjustment element 34 are controlled are stored in a familiar manner in control unit 32, which contains a microprocessor with associated storage devices. Design and function of individually illustrated assemblies and their interaction are in fact familiar and therefore not explained in detail.
A method and an apparatus is disclosed in DE 103 23 567 A1; this serves the modulation of torque capable of clutch transmission, in particular during the coupling of clutch when starting the vehicle, and thus correcting chatter oscillations. In doing so, the torque is modulated in dependence upon a filtered variable derived only from the rotation speed signal of the clutch disc or transmission input shaft. The filtered variable is calculated by smoothing the rotation speed signal of the transmission input shaft a multiple times versus a time duration, which is equal to the duration of chatter vibration, as well as by multiplication with a correction factor.
In order to decouple the vehicle's drive train from engine-excited oscillation, work is underway to operate an automated clutch with slight slip in certain rotation speed ranges.
Isolation reached by slip can considerably enhance comfort. At the same time, the differential rotation speed at the clutch must be set accurately. Too large a speed difference leads to increased energy input and lining wear; too small a speed difference can lead to a sticking clutch and hence reduced comfort. In the usual approach, trial is made to adjust the speed difference by means of a control system in that the transmittable clutch torque is modulated. To calculate the slip, differential is established between the engine speed or the clutch input shaft speed and the transmission input speed or the clutch output shaft speed. To avoid feedforward of drive train oscillations by the controller, particularly chatter oscillations, it is necessary to eliminate the chatter oscillations most extensively from the transmission input speed. A pure PT1-filter is unsuitable for this purpose, since this filter only achieves sufficient smoothing of the transmission speed only at the expense of too large a phase angle between the engine and the transmission speed. The invention is based on the task to provide a method and a device for controlling the slip of a clutch, with the one or the other demands particularly with respect to filtration of the speed signal of the transmission input speed sensor:
Chatter oscillations with typical chatter frequency for the respectively selected gear must be suppressed; the filtered speed signal at constant acceleration should be similar to a PT1-filter, after finite time it should have a slight, adjustable phase position relative to the engine speed; during load change and gearshift, overshoot and undershoot should appear as little as possible.